Humidifier



936- w. B. HODGE @123 HUMIDIFIER File d June 22, 1932 2 Sheets-Sheet 1 Fig.1.

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William B. Hodge b /wgwym ATTys.

Patented Get. 13, 1936 HUMIDIFIER William E. Hodge, Charlotte, N. 0., assignor to Parks-Cramer Company, Fltchburg, Mass a corporation of Massachusetts Application June 22, 1932, Serial No. 618,677

'1 Claims. (oi. ass-44 This invention relates to an improved humidifier of the self-contained type especially adapted for use in dwellings, school-houses, offlces, hospitals, and non-industrial service in general. The device is characterized by the simplicity of its elements, all of which are readily accessible for such attention as they-may require.

It is the general object of the invention to combine in one compact unit the means essential to the generation of a continuous current of air that passes through the interior of the unit in a predetermined path that includes a compartment containing spray-generating means. capable of atomizing water to a degree so fine that the air current may thus be charged not only with vapor produced by spray evaporation, but also with additional fine spray carried in mechanical suspension by the air current, and adapted immediately to evaporate upon distribution into the outside air. The presence of this fine spray or mist in the air current escaping from the device over and above the vapor with which the current is charged effects a corresponding increase in the mechanical efliclency and evaporative capacity of the device with consequent advantage.

A further object of the invention is the provision of adjustable means for controlling the rate at which the current of air with its burden of moisture is discharged, thus adjustably controlling the evaporative capacity of the device.

A further object of the invention is to provide an automatic regulator that is sensitive to the humidity of the air external to the device and operable to limit the supply of moisture in response to humidity rising above a predetermined standard and to increase the delivery of moisture in response to humidity falling below said standard, the regulator itself being adapted f,or assembly with the device as a part of the unit structure.

A humidifier embodying the invention is illustrated in the accompanying drawings, in which,

Fig. 1 is a view, mainly in vertical longitudinal section, of a preferred form of humidifier;

Fig. 2 is a plan view of the same, the cover being omitted;

Fig. 3 is a view, mainly in vertical section, of

,a regulator operable by a longitudinally expansible hygroscopic element for electrically controlling the operation of the humidifier; and,

Fig. 4 is a view, partly in section, of a modifiediorm of instantaneous switch mechanism operable by the longitudinal expansion of the hygroscopic element to control the operation of the humidifier.

The humidifier proper preferably consists of 5 a substantially rectangular casing having a bottom l, side walls 2 and 3, and ends 4 and 5, composed of any suitable water-proof and non-corrosive material such as certain sheet metal alloys that have suitable properties. The casing is provided with a removable cover 6, preferably composed of the same or similar materials as the main casing. The bottom, side and end walls of the casing constitute a water-tight tank suitable to contain a body of water I.

Substantially midway between the end walls of the main casing is a transverse vertical partition connecting the two side walls and dividing the main easing into two compartments. Theupper portion of this partition is preferably 2 composed of a sheet metal wall 8 extending from the top of the casing downwardly to a point substantially midway of the top and bottom. Below this point the partition comprises a screen 9, preferably of sheet metal or netting and pref- 5 erably positioned in vertical guideways ill attached to the side walls of the casing to provide for its convenient removal for cleaning.

One of the said two compartments, hereinafter called the inlet compartment, comprises an upper chamber hereinafter called the motor chamber, and a lower chamber hereinafter called the "spray chamber, which are separated from each other by a horizontal partition or deck ii. The deck ii may be supported in any suitable manner. As illustrated herein, it is of sheet metal integral with the upper wall 8 of the vertical partition and extends horizontally across the inlet compartment and is bent, downwardly to provide a vertical supporting wall 4o 02 which rests upon the bottom of the casing. Side walls may also desirably be bent down similarly to insure a rigid support for the deck. The deck is provided with a central annular opening to permit the insertion and removal of mechanism for supporting a motor and mechanism operated thereby 'for producing a spray and generating a current ,of air operable to deliver the saturated air with fine particles of moisture suspended therein from the outlet chamber in a manner which will hereinafter be more fully described.

A pipe fitting i3 is mounted in the Wall of the outlet compartment near the bottom thereof and. is provided with a ball float cool: of the usual type having a ball l4, and operable to maintain a body of water in the bottom of the casing at a substantially constant level in both the inlet and outlet chambers. An inlet pipe l5, preferably having a strainer l6 therein, and connected to a suitable source of water supply, serves to furnish a constant supply of water to the reservior within the casing.

Within the outlet compartment, and preferably attached to and extending through the same side wall thereof as the water supply fitting above described, is a fitting l I located slightly above the water level to provide for the escape of water to waste in case of faulty operation of the ball cock.

In the inlet compartment and preferably in the same side wall of the main casing with the water connections to the outlet compartment, is an inlet opening l8 communicating with the motor compartment for the purpose of admitting air thereto from outside of the casing. In the upper portion of the side and end walls of the outlet chamber are one or more outlet openings IQ for the escape of air therefrom in such direction as may be preferred, and another outlet opening may also be provided, if desired, in the cover 6 of the casing immediately above the outlet compartment. Each of these openings desirably is provided with a removable damper or gate which may be formed of sheet metal having an offset tongue 2| adapted to be inserted through the opening and of such weight as to maintain the gate 2!) closed when thus in-- serted. Any one or all of said openings may be utilized for the escape of humidified air from the outlet compartment.

Desirably means are provided for adjusting the effective area of the screened opening through which the humidified air and mist is delivered from the spray chamber. In the preferred construction illustrated a sheet metal gate 22 is mounted to slide in front of the screen 9 and is provided at its upper end with a laterally extending flange 23 by means of which it may be raised and lowered. In order to hold the screen in adjusted positions it is provided centrally with a series of holes adapted to engage a headed stud 24 projecting from the partition 8. By suitable vertical adjustment of the gate 22 the rate at which the current of air with its burden of moisture is discharged may be controlled.

Supported on the deck I I, which separates the motor chamber from the spray chamber, and within the annular opening in the deck, is provided an annular partition or hatch having a cylindrical wall 25 provided at its upper end with an annular flange 26 adapted to rest upon the deck II, and having at its lower end an upwardly inclined bottom 21 with a circular opening 28 therein providing an air intake to a fan. An annular vertical wall 29 extends downwardly from the bottom 21 in proximity to the plane of the lower edge of said opening preferably to the lower plane of said bottom. The diameter of the cylindrical wall of the hatch is slightly less than the diameter of the annular opening in the deck to permit the removal of the hatch and the mechanism supported thereby, and a rubber or fibrous cushion 30 preferably is interposed between the flange 26 and the deck II to prevent the transmission of audible vibration to the walls.

An electric motor 3| is mounted axially above and concentric with the annular opening in the hatch and preferably is supported upon the bottom of the hatch by three equally spaced inverted U-shaped flexible supports 32 which bear upon the bottom of the hatch and desirably are riveted thereto. The shaft 33 of the motor extends vertically downwardly through and concentric with the opening in the hatch and has fixedly attached to it below and in proximity to the opening a horizontal fan 34 having a diameter slightly less than that of said opening.

The motor shaft has secured to it below'the fan a hub 35 which supports a circular sprayproducing disk 36 which preferably is inclined slightly upwardly and has at its periphery a more steeply inclined flange 31. The disk preferably is composed of soft non-corrosive sheet metal, or of any suitable thin material adapted to be relatively noiseless when in operation through the absence of resonance. A hollow truncated conical member 38 extends downwardly from the hub or disk into the body of water in the lower portion of the casing, and a series of apertures 39, extending through the hub or disk and located adjacent the inner wall of the conical member, provide means by which water will be carried by centrifugal action when the disk and conical member are in rotation to the upper surface of the disk.

Resting upon and attached to the bottom of the spray compartment is a cylindrical collar 40, preferably composed of corrugated sheet metal and extending above, outside of and concentric with the lower end of the conical member. The collar is provided with one or more openings 4|, preferably in its lower edge, to permit free passage of water therethrough. The arrangement is such that when the motor is in operation the proximity of the corrugated surface of the collar tends to prevent the formation of a large whirlpool and consequent retreat of the water level from contact with the lower end of the cone; Under operative conditions the presence of the stationary body of water outside the collar and its static head maintains contact between the water within the collar and the moving lower end of the cone.

Supported on the bottom of the spray compartment by another and larger concentric collar 42 is an inverted conoidal annulus 43 composed of corrugated metal flaring upwardly and outwardly with its circular periphery slightly above and outside the peripheral flange 31 of the centrifugal disk 36. In the bottom of the collar which supports said annulus are one or more openings adapted to permit the free passage of water therethrough, thus providing for the maintenance of the water level throughout the bottom of the spray chamber.

The arrangement as a whole is such that water admitted to the casing by the ball cock is maintained at the same level in both the inlet and outlet compartments, but will remain slightly higher than the foot of the lifting cone 38 when the motor is in operation. When the motor is energized the rotation of the motor shaft causes water to be lifted by centrifugal force along the inner wall of the cone and through the apertures 39 to the upper surface of the disk. Under further action of centrifugal force the water adhering to the surface of the disk spreads outwardly in a thin film to its peripheral edge from which it is discharged outwardly and separated into fine particles of spray that are hurled in a direction tangential to the edge of the disk against the surface of the coraosmae rugated annulus surrounding the disk. so that the force of impact results in further and finer atomization of the major portion of the water.

The angle of incidence at which the particles of spray strike the annulus is such that the lighter and more finely atomized particles pass upwardly and outwardly over the edge of the corrugated annulus, while such heavier particles as adhere to the corrugated surface of the annulus collect and flow downwardly into the body of water at the. bottom of the chamber.

The rotation of the motor causes the fan to generate a strong current of air which follows a predetermined path through the space within spray and saturation of the air.

Passing outwardly through the space between the bottom of the hatch and the upper periphery of the annulus the air current then traverses the outer space within the spray chamber escaping through the screen into the lower part of the outlet chamber and thence through the outlets therefrom into the outer air.

During the time that elapses between the delivery of the spray into the air current and its escape to the outer air, the air becomes saturated with water vapor by the natural evaporation of spray. Owing to the rapidly changing direction of the air current while traversing the spray chamber any particles of heavy spray that may be present are extracted either by deposition upon the side walls and screen surfaces or by settling upon the water surface in one or the other compartment by the action of gravity. At the moment of its escape into the outer air, the air current therefore contains only such minute particles of the finest spray as have so little mass that they are capable of floating in the air current in mechanical suspension and are thus carried upward from the lower portions of the outlet compartment to the outlets in its upper portion.

A deflector 44 is secured to the inner surface of the outlet chamber above each of the outlets is extending downwardly and inwardly from the upper edge thereof. These deflectors serve to'impart an .upward direction to the air current escaping from the outlets i9 and they also serve to divert drops of moisture that may collect as'the result of condensation above the 1 outlets and prevent particles of such moisture from being blown outward with the aircurrent as might otherwise occur. v

The motor 3i preferably is provided with flexible electric conductors 55, @533 of relatively short length terminating in a plug it of the usual type which is removably connected to a complementary socket ll preferably attached to the interior surfaceof one of the walls of the motor compartment. An electric current is supplied to the motor 3| through a cable 58, one of the conductors 49 of which is connectedto a switch 50 from which a conductor 49a: leads to one of the terminals of the socket M. The other conductor 5i of the cable 48 may lead directly to the other terminal of the socket 41, but preferably leads thereto through an automatic regulator which is operableby variations in the condition of the humidity of the air, as will hereinafter be more fully described.

By reason of the fact that the motor and the fan and centrifugal distributing disk carried by its shaft are all supported upon the removable hatch, this entire mechanism can be conveniently lifted out of the casing upon detachment of the plug 46, thereby rendering all the running gear of the assembly conveniently accessible for such care as they may require, and at the same time rendering all parts of the interior of the casing itself accessible for cleaning, or such other care as may be required.

The humidifier is adapted for either temporary or permanent mounting on a radiator or on any convenient support and may be either temporarily or permanently connectedwith any available source of water supply and waste that'is convenient.

A further object of the invention, as above stated, is to provide automatic regulating means sensitive to the humidity of the air and operable alternatively to interrupt or resume the operation of the humidifier in response to humidity rising above or falling below a predetermined value. Desirably the regulator is attached to the outside of the wall of the humidifier casing adjacent to the inlet opening i8 in such manner i that the sensitive member of the regulator will be located in the direct path of the current of air approaching and flowing into the motor compartment. The sensitive member of the regulator may be composed of any hygroscopic material that will respond to changes in the humidity of the surrounding atmosphere with elongation or contraction having sufilcient force to actuate a switch or other suitable means for controlling the supply of energy which motivates the humidifier.

The preferred constructions which are illustrated herein comprise a bracket 52 which is secured to the rear wall 3 of the intake compartment a short distance below the inlet 68 and supports a vertical tubular housing 53 having a plurality of apertures 54 therein adapted to permit the air to circulate freely within the housing.

The housing 53 has at its upper end a head 55 head, the screw ,being held against rotation relatively to the adjusting member 59 by a set screw Hi. The lower end of the screw 55, which as illustrated herein is conical. extends into the central opening in a bushing 62 which is abutted' by the enlarged upper end 53 of a hygroscopic member sensitive to variations in humidity in the air.

The hygroscopic sensitive member shown in the present embodiment is a cylindrical body composed of any suitable wood, such as bass wood, extending axially or the housing 53 and provided with a central enlargement 65 which, like the enlarged end 63, slidably fits within the housing 53 and may be adjusted downwardly by rotation of the rotatable adjusting member 58 in a clockwise direction. Undue rotation of the adjusting member 58 is prevented by a screw 86 mounted in the wall of the casing and extending into a slot or recess formed by cutting away a desired portion, such, for example, as one-half of the lower end of the adjusting member 58, thereby providing shoulders 61 which will limit the rotative movement of the member 58. Desirably the lower central portion of the adjusting member 58 is bored to provide a recess 68 and a spring 69, located in said recess and abutting at its lower end against said head and at its upper end against the end wall of the recess, produces suiiicient frictional resistance to insure retention of the adjusting member 58 in any desired position of adjustment.

The lower end of the hygroscopic member 64 is seated in the enlarged socket end 10 of a pin H which is slidably mounted in a lower head 12 fixedly secured to the housing 53. The lower end of the pin 1| engages the arm 13 of a lever which is operable to actuate a special switch adapted to instantly make or break a circuit of the service current supplied to the motor.

Inasmuch as an electric current having a substantially high voltage of usually 110 volts is required to operate humidifiers of the character herein described, or to control the operation of valves of humidifying systems, and inasmuch as the extent of movement of hygroscopic elements required to maintain a substantially uniform condition of humidity is very slight, it has heretofore been considered generally necessary to provide relay mechanism intermediate of the hygroscopic element and the switch controlling the service current to supply sufficient energy properly to actuate the switch which controls the service current.

One of the objects of the present invention is to provide a switch mechanism for the service current which will be directly operated by the expansion of the hygroscopic element to open the service current when the humidity reaches or exceeds a predetermined degree, andwhichwill close said switch promptly when the humidity fall below said predetermined degree.

A further object or the invention is to provide switch mechanism of this character which will operate instantaneously and avoid any substan-- tial sparking upon the breaking of the circuit.

In the construction illustrated in Fig. 3, the lever 13 is in the form of a bell crank lever pivotally mounted upon a stud 14 in the lower end of a cylindrical housing 15 which is also mounted in the bracket 52. The other arm 16 of the bell crank lever, which is fixedly secured to the arm 13, is provided at its upper end with an offset fiat spring Tl having an L-shaped end 18 which bears against astem 19 of an integral glass bellows 89 of special shape and temper, which extends upwardly into an integral cylindrical container 8|, the upper end of which is provided with an inwardly extending solid boss 82 through which conductor wires 83 and 84 extend. The cylindrical container 8| is highly evacuated. The end of the conductor 84, which extends through the boss, is reversely bent to provide an angular contact 85. The end of the conductor 83 has secured to it a spring 86 provided with a contact block 87 adapted normally to engage the member 85. The block 8'! is engaged by the upper end of the stem 19. The glass bellows 88, by reason of its shape and temper, is highly elastic and a slight movement of the stem 19 produced by lateral pressure upon its lower end and transmitted from the hygroscopic member through the bell crank and spring 11, will cause the block 81 to separate from the contact 85. The spring 88 causes positive connection between the contacts when no pressure is applied to the stem 3|.

Inasmuch as the switch members are in vacuum the separation of the contact members will not cause substantial sparking and there is, therefore, no exposed spark or are to induce a fire hazard when operating in an inflammable atmosphere. The construction is such that a movement of .02" at the upper end of the stem II will operate the enclosed contacts and such making and breaking of the service current may be made with great frequency without injury. The action of the switch is instantaneous so that a very accurate control of the electric circuit and the operation of the motor, or other electrical devices employed in the humidifying system, is highly efllcient.

A diagrammatic illustration of an electric circuit is shown in Fig. 3 from which it will be seen that the electric current passes, when the circuit is closed, through the conductor 49 of the cable 48 to the switch 50, thence through the conductor 49 and through one of the terminals of the socket 41 and conductor 45 to the motor 3|. The current passes from the motor through the conductor 45cc, thence through the other terminal of the plug socket 41, the conductor 83, thence through the spring 86 and contact block 81 to the contact member which are located in the vacuum chamber, and from the contact member 85 to the conductor 84 which is connected to the other conductor 5| of the supply cable 48.

In Fig. 4 a different form of instantaneous switch is illustrated. In this construction a rectangular casing 98 is secured to the lower end of the apertured housing 53, heretofore described, and the pin H at the lower end of the hygroscopic element engages the arm 9| of an L-shaped lever which is fulcrumed upon a stud or screw 92 mounted in said housing. The arm 9| is held firmly in engagement with the pin H by a coiled spring 93, one end of which is connected to the offset end 94 of the lever arm 9|, and the opposite end of which is secured to a stud 95 upon said housing. The opposite arm 96 of the lever 9| is provided with an offset end portion 91 which engages a pin 98 which is slidably mounted in the cover 99 of an insulated container having a base Hill of insulating material with binding posts IM and H12 seated therein. The opposite sides ofthe cover are provided with downwardly extending ears I03 adapted to be secured to the base by suitable screws I04.

The service conductors 83 and 84 are electrically connected to the binding posts |0| and I02 respectively.

The switch proper comprises a resilient flexible member that is subject to an initial stress which operates normally to maintain the switch in an open condition and also to close the switch instantaneously when pressure is applied to the flexible member by the pin 98 in value sufiicient to overcome said stress; also to cause the switch instantaneously to reassume its normally open condition when the value of the applied pressure falls below that value which is suflicient to cause a closure. Preferably the switch comprises an initially warped or distorted spring plate Hi one end of which is fixedly secured to the binding post NH and a complementary terminal I06 which is secured to the binding post it? with which the free end of the flexible member contacts when in closed condition. The plate Hill of insulating material underlies the free end of the spring plate I05. The initial warp or distortional stress to which the flexible member tilt is subject is such as to maintain its free end in contact with the insulated plate ill! in the absence of pressure on the pin H, thus establishing a condition of normal closure for the switch proper.

In a regulator of the type disclosed in the present embodiment, it is desirable to make provision such that the hygroscopic element may expand or contract freely in response to changing humidity without being subjected to any materially greater strain or resistance than is imposed upon itby the load required to produce actuation, thus avoiding such injury to the element as might otherwise occur.

In the embodiment of the invention illustrated in Fig. 4 the lever 9i9t is therefore interposed between the hygroscopic element St and the switch pin 98 and the spring 93 is attached to the lever under tension in an arrangement such as to maintain the switch. in a closed position by applying pressure to the flexible member tub-which is transmitted'by the lever 9i-9t through the pin 98, this condition of the lever and switch being maintained so long as the lever is affected only by the tension of the spring 93. Hygroscopic elements of other material than wood may be employed in a. similar organization for the purpose of and within the scope of the invention.

During periods when the switch is closed the completion of the circuit through the motor actuates the humidifier to produce and saturate a spray-laden current of air as heretofore described and the resulting increase in the humidity of the surrounding air ultimately causes elongation of the hygroscopic member 64 causing the pin ii at its end'to press downwardly upon the arm 9! of the lever thereby raising its opposite arm 96 and relieving the pressure imposedupon the pin 98 which instantly permits the warped plate H25 by reason of its resilience to snap out of contact with the terminal ilit into engagement with the supporting insulated member ml, thereby instantly breaking the circuit. The spring action of the warped plate is practically instantaneous and by reason of the relatively large area of contact between the plate M and the terminal tilt and the instantaneous separation of the plate from the terminal, arcing is effectively prevented. Moreover, by reason of the fact that the switch mem bers arewholly enclosed within the insulated container Hit there is no possibility of an exposed spark or arc which would induce or constitute a fire hazard.

Opening of the switch having thus been accomplished and delivery of moisture by the humidifier having thus been interrupted, the humidity of the surrounding air will gradually fall in response to which the hygroscopic member at will contract, the lever arm 9% which is in contact with it meanwhile rising as a result of the tension of spring 93 depressing the lever arm 96 and applying pressure through the pin 98 upon the switch member M5 which when attaining the corresponding value will cause instantaneous closure of the switch and resumption of the delivery of moisture.

It is to be noted that'during periods when the hygroscopic member 64! is expanding in response. to increasing humidity it encounters no 5 resistance other than the elastic resistance due to the tension of the spring, which is an important characteristic of the type of regulator herein disclosed.

It will thus be apparent that by reason of the present invention a very eflective control for the humidifier is provided and that by reason of the fact that the hygroscopic element is positioned directly'in the path of the air entering the humidifier casing, an exceedingly accurate control of humidificatiorr of the air oi the enclosure is secured.

It will be apparent that a controller or the type disclosed may be applied to electrically motivated humidifying means in a variety of circumstances within the scope of the invention.

It will also be understood that the particular embodiment of the invention disclosed herein is of an illustrative character and that various changes in form, construction, and arrangement of parts may be made within the spirit and scope of the following claims.

Having thus described the invention, what is claimed as new, and desired to be secured by Letters Patent, is:

1. Humidifying apparatus comprising humidifylng means controlled by a commercial electric circuit having a safety switch construction comprising an apertured tubular housing having a rigid hygroscopic element subject to elongation and contraction in response to increase and decrease in the humidity of the air mounted in said tubular housing and having centrally of its length an enlarged guiding portion slidably fitting within said housing to insure accurate movement thereof in the direction oi the axis of said housing, a casing rigidly connected to said housing having therein a closed insulated container, a non-sparking switch within said insulated container having cooperating fixed and resilient metal contact members connected in said circuit, and means operable upon elongation of said hygroscopic element to actuate said switch.

2. Humidifying apparatus comprising humidiiying means controlled by a commercial electric circuit having a safety switch construction comprising an apertured vertical cylindrical housing having a hygroscopic element subject to elongation and contraction in response to increase and decrease in the humidity of the air mounted in said cylindrical housing, means connected to the lower end of said hygroscopic member and guided by said housing to move in the direction of the axis of said housing, a casing rigidly connected to said housing having therein a nonsparking switch in said electric circuit enclosed in an insulated container, and means operable by the means connected to the lower end of said hygroscopic member operable upon elongation of said hygroscopic member to actuate said switch.

3. Humidifying apparatus comprising humidifying means controlled by a commercial electric circuit having a safety switch construction comprising an apertured vertical cylindrical housing having a hygroscopic element subject to elongation and contraction in response to increase and decrease in the humidity oithe air mounted in said cylindrical housing, a pin connected to the hit ' cause the actuation of said switch.

4. Humldifying apparatus comprising humidifying means controlled by a commercial electric circuit having a safety switch construction comprising an apertured vertical cylindrical housing having a hygroscopic element subject to elongation and contraction in response to increase and decrease in the humidity of the air mounted in said cylindrical housing, a closed casing, of insulating material rigidly connected to said housing, a non-sparking snap-switch in said electric circuit enclosed within said insulating casing, and means including a pin connected to the lower end of said hygroscopic element and movable axially of said housing operable upon elongation of said hygroscopic element to actuate said switch.

5. Humidifying apparatus comprising humidifying means controlled by a commercial electric circuit having a safety switch construction comprising a vertical tubular apertured housing having a head fixedly secured therein, a hygroscopic element subject to elongation and contraction in response to increase and decrease in the humidity of the air mounted in said tubular housing, a pin connected to the lower end of said hygroscopic element, means for guiding said pin in the direction of the axis of said housing upon elongation of said hygroscopic element, means including a member having screw threaded engagement with said head for adjusting the position of said hygroscopic member in said housing, and anon-sparking switch having cooperating fixed and resilient metal contact members in said electric circuit, a closed casing of insulating material enclosing said switch, and

means operable by the pin which is connected to the lower end of said hygroscopic member to actuate said switch upon elongation of said hygroscopic element.

6. Humidifying apparatus comprising humidifying means controlled by a commercial electric circuit having a safety switch construction comprising an apertured vertical cylindrical housing having a hygroscopic element subject to elongation and contraction in response to increase and decrease in the humidity of the air mounted therein, a casing rigidly connected to the lower end of said housing, a snap switch in said electric circuit enclosed within said casing having a flexible resilient member subject to distortional stress normally acting to close said switch, means connected to the lower end of said hygroscopic element operable upon elongation of said hygroscopic element so to vary said distortional stress as to cause the resilience of said flexible switch member instantly to open said switch.

7. Humldifying apparatus comprising humidifying means controlled by a commercial electric circuit having a safety switch construction comprising a vertical, cylindrical apertured housing having an adjusting screw mounted in the upper end thereof, a hygroscopic element composed of a rigid material subject to elongation and contraction in response to increase and decrease in the humidity of the air mounted in said cylindrical tubular housing to abut at its lower end against a member movable in the direction of the axis of said housing by elongation of said hygroscopic element and to abut at its upper end against said adjusting screw, 21 non-sparking switch in said electric circuit, and means operable by the member abutting the lower end of said hygroscopic element to actuate said switch upon elongation of said hygroscopic element in organization suitable for the adjustable positioning of said hygroscopic element with respect to said switch.

WILLIAM B. HODGE. 

